I did this last season on the same helmet. You need threaded inserts and the screws that go into them. They don't need to be made by Briko. Just head to a good shop and ask for some. To install then, just drill snug holes and press-fit them in and you'll be good to go.

I guess I am revealing my structural engineering incompetence here. We just drilled holes and attached the chin guard. That was two seasons back. Will these threaded inserts be better in protecting the helmet? I would think you'd just have to make bigger holes then to accommodate the insert, thereby further weakening the helmet?

The part of the helmet that you drill isnt an integral part of the head-saving section of the helmet. Ihave seen it done a lot and never seen any adverse affects from it. I have seen helmets crack in half, but not from drilling holes to attach a chin bar. As long as the holes are clean and no cracks develop during the drilling process, you should be okay. I have seen it done with and without threaded inserts - and even with hardware store materials.
Later
GREG

I guess I am revealing my structural engineering incompetence here. We just drilled holes and attached the chin guard. That was two seasons back. Will these threaded inserts be better in protecting the helmet? I would think you'd just have to make bigger holes then to accommodate the insert, thereby further weakening the helmet?

Really depends on the helmet. I use teenuts on some, and other types of speednuts on others. Here is a teenut: